Rotor ships exploit the Magnus effect to generate wind propulsion. In essence, the Magnus effect dictates that a rotor in a wind stream will generate low and high pressure regions on either side of the rotor tangential to the direction of the wind stream. Thus, a powered rotor can propel a ship in a wind stream by harnessing some of the energy of the wind stream and redirecting it to propelling the ship.
The rotor ship was invented by Anton Flettner in the early 1920s. Flettner constructed the first rotor ship, the Buckau, in 1924. The Buckau proved the viability of rotor ship technology on its maiden voyage in February 1925, crossing the North Sea from Danzig to Scotland. Despite being dogged by extremely poor weather, the voyage was a success and proved that Flettner rotors were sufficiently effective and durable for ship propulsion, even in the harshest conditions.
Although Flettner had demonstrated that Magnus propulsion was a viable shipping technology, the rotor ship did not achieve mainstream success in the 20th century shipping industry. Conventional water propeller systems remained the mainstream choice, in part because those systems are simple and their performance is not dependent on weather conditions. Furthermore, fossil fuels generally remained inexpensive during this era, at least compared with the costs associated with more exotic ship designs that improved efficiency.
Those market realities began to change in the early 21st century. Fuel prices increased as did political pressure to reduce fuel consumption and emissions. Furthermore, the late 2000's global recession placed incredible pressure on the shipping industry. The total volume of cargo traffic decreased significantly, as did demand for new ships. Shipping companies that have survived in this market are very interested in cutting costs wherever possible, including fuel costs.
These paradigm shifts have renewed interest in rotor ship technology because of potential fuel savings and emissions reductions. Of particular interest are retrofittable rotor systems, because of the aforementioned reduction in new ship production. However, the old rotor designs of the early 20th century and similar contemporary designs leave much to be desired.
The primary problem is the space taken up on the deck by having several rotors. This is especially problematic on ships that were not originally designed to use flettner rotors (retrofitted ships). Attempts have been made to get around this problem, such as retractable telescoping rotors or foldable rotors. However, these systems are complex, potentially fragile in extreme weather conditions, and do little to save deck space.
There remains a need in the art for a truly modern rotor ship system that can be incorporated on modern non-rotor ships with minimal interference with their normal operation. Such a design could result in huge fuel consumption and emissions reductions because it could be incorporated on a large portion of the global shipping fleet.